Polyphenylene ether (PPE) is a thermoplastic, linear, non-crystalline polyether made by the oxidative condensation of 2,6-dimethylphenol in the presence of a copper-amine-complex catalyst.
PPE, also called polyphenylene oxide, is known by those skilled in the art for its high heat resistance and for its flame retardance as a char former, with a Limiting Oxygen Index by ASTM. D 2863 of ˜29%, which means PPE is not flammable under normal atmospheric conditions. Typically the glass transition of PPE ranges from ˜210° C. to ˜215° C. depending on its molecular weight.
Commercial PPE is well known, preferably in the form of a miscible blend of PPE and polystyrene, marketed as Noryl® resin from Sabic Innovative Plastics.
In addition to the use of PPE as a primary resin, PPE can also be used as an additive for epoxy resins to improve toughness and as an additive to styrenic copolymers to increase heat distortion temperature. In these additive applications, it is often desirable to have and use a lower molecular weight PPE (Mn ˜10,000-20,000 g/mole) or in some instances even lower. Such PPE materials are commercially available from Sabic but are considerably more expensive than the conventional molecular weight PPE (Mn ˜34,000-53,000 g/mole) because they are generally prepared from such conventional molecular weight PPE and then subjected to molecular weight reduction methods. Moreover, these commercially available low molecular weight PPE resins are prepared using a solvent-based process. Unfortunately, no matter how well the production occurs, there is always the possibility of residual amounts of solvent remaining in the resulting low molecular weight PPE resin.